Large diameter, underwater pipes are required to transport large volumes of fluid under low pressure, for applications such as ocean thermal energy conversion (“OTEC”), algae production for biomass energy, and fresh water transport between regions along coastlines, among other purposes.
These pipes, which extend vertically to significant ocean depths, encounter at least one ocean current. Ocean currents impose drag forces on a structure. Relatively larger structures present a relatively greater amount of area to the current and, as a consequence, experience a relatively greater drag force than a smaller structure from a given current.
The drag forces impose bending loads on the structure, with longer structures experiencing more severe bending stresses. Ocean current drag forces and the bending stresses produced thereby therefore present a significant engineering challenge to the manufacture of deep-water pipes.
Conventional large-diameter pipes are usually constructed as rigid or semi-rigid structures that are self supporting or supported via internal stiffeners. The resulting pipes are not mechanically compliant, and consequently require substantial structure to resist ocean currents or other externally-imposed forces without deflecting or fracturing. Materials in conventional pipes are loaded in both tension and compression, thereby increasing the degree of structural complexity because of the need to resist buckling of the material under compression.